The present invention relates, in general, to electronics, and more particularly, to methods of forming semiconductor devices and structure.
In the past, various methods and structures were utilized to produce resonant switching power supply converter systems. The resonant switching power supply converter system generally used an isolation transformer that included primary and secondary windings. A capacitor was connected in series with the primary winding so that the capacitance and the inductance of the inductor formed a resonant circuit having a resonant frequency. The isolation transformer was formed so that there was a loose inductive coupling between the primary and secondary windings which resulted in a low coupling coefficient between the primary and secondary windings. This loose inductive coupling formed a parasitic inductor in series with the primary winding inductance which was often referred to as a leakage inductance that represented the coupling between the secondary and primary windings. A rectifier diode, such as a Schottky diode, usually was coupled in series with the secondary winding in order to form an output voltage from the currents induced into the secondary winding.
In some embodiments, a synchronous rectifier transistor was coupled in parallel with the rectifier diode in order to increase the efficiency of the power supply system. The synchronous rectifier transistor usually was controlled responsively to the current through the rectifier diode that was in the secondary. A secondary side control circuit usually was configured to control the synchronous rectifier. These secondary side control circuit usually were designed to turn the synchronous rectifier on when the secondary current increased to a value that was just above zero and was designed to turn the synchronous rectifier off when the current through the rectifier diode decreased to a value that was zero. One problem with such configurations was that the efficiency of the series resonant switching power supply system decreased as the switching frequency of the transistors on the primary side increased to a value that was equal to or greater than the resonant frequency formed by the capacitor and the leakage inductance of the transformer. This type of operation also increased electromagnetic interference.
Accordingly, it is desirable to have a series resonant switching power supply system that can operate near above the Series resonant frequency with a high efficiency and with a low electromagnetic inference.
For simplicity and clarity of the illustration, elements in the figures are not necessarily to scale, and the same reference numbers in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. As used herein current carrying electrode means an element of a device that carries current through the device such as a source or a drain of an MOS transistor or an emitter or a collector of a bipolar transistor or a cathode or anode of a diode, and a control electrode means an element of the device that controls current through the device such as a gate of an MOS transistor or a base of a bipolar transistor. Although the devices are explained herein as certain N-channel or P-Channel devices, or certain N-type or P-type doped regions, a person of ordinary skill in the art will appreciate that complementary devices are also possible in accordance with the present invention. It will be appreciated by those skilled in the art that the words during, while, and when as used herein relating to circuit operation are not exact terms that mean an action takes place instantly upon an initiating action but that there may be some small but reasonable delay, such as a propagation delay, between the reaction that is initiated by the initial action. The use of the word approximately or substantially means that a value of an element has a parameter that is expected to be very close to a stated value or position. However, as is well known in the art there are always minor variances that prevent the values or positions from being exactly as stated. It is well established in the art that variances of up to at least ten per cent (10%) (and up to twenty per cent (20%) for semiconductor doping concentrations) are reasonable variances from the ideal goal of exactly as described.